The present invention relates to rare earth resin magnet used in a motor, its magnet rotor, and a magnet motor using the same.
FIG. 8 is a sectional structural view of an annular magnet motor having an output of several watts (W) or less. In FIG. 8, the magnet motor comprises a substrate 1, an armature core 2 having a plurality of salient poles, a drive winding 3 wound around each salient pole, a bearing 4, a rotary shaft 5, a rotor frame 6, and an annular magnet 7. The annular magnet 7 is affixed to the inner peripheral wall of the rotor frame 6. The annular magnet 7 has a multiplicity of magnetized poles.
This conventional annular magnet, and the conventional motor using such conventional magnet are explained below.
The annular magnet used in the conventional magnet motor was made from a flexible sheet-shaped bonded magnet. The flexible sheet-shaped bonded magnet is composed of a mixture of ferrite magnetic powder and rubber-like resin. The flexible sheet-shaped bonded magnet is cut in bands. The flexible sheet-shaped bonded magnet cut in bands is affixed to the inner peripheral wall of the rotor frame while being curled in a rink shape. The flexible sheet-shaped bonded magnet in a cut ring shape is disposed oppositely to the salient pole surface of the armature core. The ferrite magnetic powder is a fine metal oxide with a particle size of 3 xcexcm or less, and the maximum energy product [BH] max. of the flexible sheet-shaped bonded magnet obtained from the ferrite magnetic powder and rubber-like resin is about 1.4 MGOe at a maximum limit. Therefore, since its magnetic force is small, the intensity of the magnetic field occurring in the space between the magnet and armature core was a relatively weak static magnetic field. Accordingly, if the flexible sheet-shaped bonded magnet containing the ferrite magnetic powder was cut in bands, the ferrite magnetic powder positioned at the cut section had little effects on the performance and reliability of the annular magnet motor. However, to satisfy the requirements for higher output and lower current consumption of the annular magnet motor, it is needed to form a potent static magnetic field in the mutually opposing space of the magnet and armature core. The magnet using such conventional ferrite magnetic powder could not build up a potent static magnetic field in the space between the magnet and armature core.
As a flexible sheet-shaped bonded magnet, a flexible sheet-shaped bonded magnet containing rare earth magnetic powder and rubber-like resin has been known.
Japanese Patent No. 2766746 (Japanese Laid-open Patent No. 5-55021) discloses a flexible sheet-shaped bonded magnet comprising a first group, a second group, and a third group. The first group include Ndxe2x80x94Fexe2x80x94B magnetic powder and (Ce, La)xe2x80x94Fexe2x80x94B magnetic powder. The second group includes natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, ethylene propylene rubber, ethylene vinyl acetate rubber, nitrile rubber, acrylic rubber, and urethane rubber. The third group includes chloroprene rubber, polyethylene chlorosulfonide, and polyethylene chloride. In each group of the first group, second group, and third group, one or more materials are selected. The magnetic powder in the first group is contained in a range of 92 to 96 wt.%. The density of this flexible sheet-shaped bonded magnet 4.9 to 5.8 g/cm3. Such flexible sheet-shaped bonded magnet is cut in bands, and curled to a ring shape, and affixed to the inner peripheral wall of the rotor frame, so as to be opposite to the salient pole surface of the armature core. Such magnet motor has been known.
A manufacturing method of flexible sheet-shaped bonded magnet disclosed in Japanese Patent No. 2528574 (Japanese Laid-open Patent No. 5-47576) comprises (a) a step of kneading Rxe2x80x94Fexe2x80x94B (R being Nd/Pr) magnetic powder and binder, (b) a step of grinding the mixture and rolling into a sheet, and (c) a step of heating the rolled sheet of magnet material to 125 to 180xc2x0 C. for 60 to 180 minutes.
However, the motor having such conventional flexible sheet-shaped bonded magnet involves the following problems (1), (2) and (3).
(1) Since the density of the flexible sheet-shaped bonded magnet is 4.9 to 5.8 g/cm31, there is a limit in the magnetic performance.
(2) The flexible binder and rare earth magnetic powder are not in mutually adhesive state, by nature. Accordingly, by the magnetic attracting force of an excited armature core, the rare earth magnetic powder drops out and scatters about. It hence causes rotation noise or rotation troubles. As a result, there is a problem in the motor reliability.
(3) The manufacturing process is complicated including the steps of processing the film by epoxy resin, overheating for vulcanizing the flexible binder, reheating the cut section, and affixing for eliminating failure in the cut section when affixing the flexible sheet-shaped bonded magnet to the rotor frame, and there is a problem in the reliability in the manufacturing process.
On the other hand, the following annular resin magnet has been known. Japanese Patent Publication No. 6-87634 (Japanese Laid-open Patent No. 62-196057) discloses an annular magnet motor using an annular resin magnet for producing a potent static magnetic field in the space opposite to the armature core. That is, the annular resin magnet includes isotropic Rxe2x80x94Fexe2x80x94B (R being Nd/Pr) magnetic powder and resin, with an outside diameter. of 25 mm or less. The density of the annular resin magnet ranges from about 5 g/cm3 to about 6.3 g/cm3, and resin magnet having a density exceeding 6.3 g/cm3 cannot be obtained. The maximum energy product [BH] max. of the annular magnet containing isotropic magnetic powder is 11 to 12 MGOe at a limit. By contrast, anisotropic magnetic powder declines in the degree of orientation of the magnetic powder as the diameter of the annular magnet becomes smaller. Accordingly, in the annular magnet motor using an annular magnet containing anisotropic magnetic powder, it was difficult to satisfy both smaller size and higher output.
For example, a flexible sheet-shaped bonded magnet containing Sr ferrite magnetic powder and rubber-like resin, and a molded annular magnet containing Rxe2x80x94Fexe2x80x94B (R being Nd/Pr) magnetic powder and binder were compared. The flexible sheet-shaped bonded magnet was cut in a band of 1.5 mm in thickness and 7.2 mm in width, and this band of flexible sheet-shaped bonded magnet curled, and affixed in a ring shape to the inner peripheral wall of a rotor frame of 22.5 mm in inside diameter. The starting torque of the annular magnet motor was 1.5 mN-m. By contrast, the molded annular magnet was compressed and molded to outside diameter of 22.5 mm, thickness of 1.10 mm, height of 9.4 mm, and density of 5.8 g/cm31, and the obtained molded annular magnet was affixed to the rotor frame. The starting torque of this annular magnet motor was 20 mN-m.
Japanese Patent Publication No. 6-42409 (Japanese Laid-open Patent No. 62-263612) discloses a bond magnet having isotropic Fexe2x80x94Bxe2x80x94R magnetic powder and binder. The binder comprises an oligomer having an alcoholic hydroxyl group in a molecular chain such as bisphenol type epoxy which is solid at room temperature, and an isocyanate regenerated form, so that the Rxe2x80x94Fexe2x80x94B (R being Nd/Pr) magnetic powder and binder are adhered and fixed to each other more firmly.
The isocyanate regenerated form is a compound obtained by adding an active hydrogen compound preliminarily to an isocyanate compound. By thermal dissociation, the isocyanate regenerated form releases isocyanate group, and the free isocyanate group reacts with an alcoholic hydroxyl group, and crosslinks by urethane bonding or the like. At this time, part of the free isocyanate group reacts with adsorbed water on the metal surface such as Rxe2x80x94Fexe2x80x94B (R being Nd/Pr) magnetic powder, and produces a urea substituent. This urea substituent produces chelate bond with a metal oxide surface layer. It hence prevents dropping or scattering of magnetic powder contained in the bonded magnet, and the performance and reliability of the annular magnet motor using such bonded magnet are assured.
Therefore, such isotropic molded annular magnet is the most effective prior art for higher output and lower current consumption of a small annular magnet motor. Generally, due to limit of design in the magnetic field forming method, it is difficult to manufacture an annular molded magnetic having a small diameter. In the manufacturing method of small annular magnet, there is a limit in the intensity of magnetic field generated in the radial direction. That is, the limit value of intensity of the magnetic field generated in the radial direction is extremely smaller than the limit value of intensity of the magnetic field generated in the axial direction. Besides, since the isotropic Rxe2x80x94Fexe2x80x94B resin magnet is limited in the content of the magnetic powder contained in the resin magnet or in the density of resin magnet, the magnetic performance of the resin magnet has its upper limit, and the magnetic performance is limited. The magnetic powder contained in such resin magnet is adhered and fixed firmly by a thermosetting binder, its recycling is difficult.
Japanese Laid-open Patent No. 5-299221 discloses a small motor using a cut-off flexible sheet-shaped bonded magnet containing rare earth-iron-nitrogen magnetic powder and styrene elastomer denatured by acid. That is, rare earth-iron-nitrogen magnetic powder and styrene elastomer denatured by acid are kneaded and rolled, and cut in short strips. The short strip is curled, and an annular magnet is formed. This annular magnet is used in the small motor. The density of this annular magnet is 5.6 g/cm3, and the maximum energy product [BH] max. is 4.4 MGOe. This flexible sheet-shaped bonded magnet containing rare earth-iron-nitrogen magnetic powder is inferior in the magnetic performance to the annular resin magnet containing isotropic Rxe2x80x94Fexe2x80x94B (R being Nd/Pr) magnetic powder and binder (density 6.2 to 6.3 g/cm3, maximum energy density [BH] max. 11 to 12 MGOe). Therefore, the motor using the flexible sheet-shaped bonded magnet containing rare earth-iron-nitrogen magnetic powder cannot obtain a potent static magnetic field in the gap against the armature core.
The rare earth-iron-nitrogen magnetic powder of Pining type is a fine powder having a single phase of Sm2Fe17N3 magnetic phase of several xcexcm. Accordingly, the Pining type magnetic powder is chemically active. Hence the rare earth-iron-nitrogen magnetic powder is exposed to the atmosphere at the cut section of the flexible sheet-shaped bonded magnet, and permanent demagnetization due to oxidation and corrosion takes place. Further, the adhesion between the magnetic powder and styrene elastomer is lowered, and dropping and scattering of magnetic powder occur.
A rare earth resin magnet of the invention comprises at least one resin of thermoplastic resin and thermoplastic elastomer, pentaerythritol stearic acid triester, and rare earth magnetic powder, in which the rare earth magnetic powder, the resin and the pentaerthritol stearic acid triester form a mutually mixed resin magnet composition, and the resin magnet composition has a specific shape.
A magnet rotor of the invention has the rare earth resin magnet.
A magnet motor of the invention comprises the above-mentioned rare resin magnet, a rotor frame, an armature core, a winding, and a rotor, in which the rare earth resin magnet has a ring shape, and the rare earth resin magnet of the ring shape is installed in the inner periphery of the rotor frame.
A manufacturing method of rare earth resin magnet of the invention comprises:
(a) a step of forming a mixture containing at least one resin of thermoplastic resin and thermoplastic elastomer, rare earth magnetic powder, and pentaerythritol stearic acid triester, and
(b) a step of forming a resin magnet molded element having a specific shape from the mixture.
Preferably, in 100 parts by weight of the resin, the pentaerythritol stearic acid triester is contained by 2 parts by weight or more.
Preferably, the rare earth magnetic powder is dispersed in the resin, and oriented in a specific direction by magnetic field orientation.
Preferably, the specific shape is a shape formed from a hot-processed resin magnet molded element.
This constitution brings about the following effects.
In a rare earth resin magnet using thermoplastic resin or thermoplastic elastomer, a rare earth resin magnet capable of enhancing the filling rate of rare earth magnetic powder is presented. It also presents a rare earth resin magnet capable of enhancing the degree of orientation of rare earth magnetic powder contained in the magnetically oriented resin magnet. It further presents a rare earth resin magnet having a magnetic performance equivalent or superior to the magnetic performance of the rare earth resin magnetic using thermosetting resin. A magnet having an extremely excellent magnetic performance is obtained. A magnet stable in the magnetic performance in a practical temperature range is obtained. A magnet having an excellent recycling property is obtained. Moreover, a magnet rotor using such rare earth resin magnet can generate a potent static magnetic field in the gap with the armature core. It presents a magnet rotor excellent in recycling performance. In a motor using such magnet rotor, the output is heightened and the current consumption is lowered.